As I've blogged about for some time now, nofollow tags are not a fit for wikis. Kevin Burton notes it is the default for all links in Google Sites:
The rel=nofollow attribute is a cancer that’s destroying the link graph.
Every URL I create is going to be blocked from link based trust metrics like PageRank? That’s just dumb. I’d rather use another wiki system that doesn’t penalize my linking behavior.
I realize that your intention is to fight spam but you should pursue and algorithmic approach. Blacklisting the entire Internet is NOT the solution.
It’s clear by now that Google uses other metrics for page ranking (almost certainly including HTTP traffic monitoring by now) so this isn’t the end of the world.
Linking is the whole point of the Internet! Creating road blocks for EVERY LINK in the system is the antithesis of a free an open web!
I'm glad Kevin is saying nofollow is not the web (outside of the blogs and comments it was designed for) and in this world view you can only give Google Juice and it doesn't give back. Such a view and action only favors those in a dominant network position.
